Fabrication of integrated circuits requires constant inspection and testing of the structures that are formed, so as to ensure that the processes are in control, the materials are not contaminated, and the structures are properly formed. As the term is used herein, “integrated circuit” includes devices such as those formed on monolithic semiconducting substrates, such as those formed of group IV materials like silicon or germanium, or group III–V compounds like gallium arsenide, or mixtures of such materials. The term includes all types of devices formed, such as memory and logic, and all designs of such devices, such as MOS and bipolar. The term also comprehends applications such as flat panel displays, solar cells, and charge coupled devices.
Typically, such inspections have been performed off line for many processes, such as for etch processes, because the substrates exiting such processes tend to outgas corrosive or contaminating materials, such as hydrogen bromide, chlorine, sulfuric acid and other materials. When inspection tools are subjected to such corrosive materials, they tend to be damaged in a relatively short length of time. Because of the relatively high cost of such equipment, such damage to the instrument is unacceptable. Thus, most inspection is done well after the process in question, such as after the substrates have been baked, cleaned, rinsed, or otherwise had the corrosive materials removed from them.
There have been some attempts to protect the inspection tools from the damaging environment produced by out gassing substrates. For example, one approach encloses the metrology device in an enclosure that includes a window, through which the measurements are made, and thus keeping the substrate separate from the measurement device. Unfortunately, some measurements cannot be made through a window in this manner.
Another approach protects individual components of the inspection tool, such as by coating circuit boards with a protective conformal coating. However, it may not be possible to apply such a coating to all of the components of the tool that are susceptible to damage from the corrosive environment. Further, methods such as these tend to reduce both measurement speed and substrate throughput. These approaches also do not address the problem of particulate contamination of the substrates and the tools, due, for example, to the formation of hydrates from the contaminating materials, such as hydrogen bromide, chlorine, and so forth.
What is needed, therefore, is a system that overcomes problems such as those described above, at least in part.